The invention relates to a system for processing plant material, and more particularly, to a system that separates fibers and woody portions of the plant material.
It has long been known that the bast fibers of various plant materials, e.g. flax, jute, hemp, ramie, kenaf, have particular utility in a wide variety of textile and industrial uses. Accordingly, many different types of machines have been used to process the material for separating the bast fibers of the plant material from the woody portions thereof. For example, machines that utilize a scutching or beating or flailing action as the primary mechanism to break-up the woody material for dislodging it from associated fibers are well-known in the art.
A problem arises with the above-referenced processes in that they can tend to undesirably damage or shorten the fibers as they are being separated from the woody portions of the plant material and thereby yield a product that has fibers that are shortened beyond their optimum length for maximizing their commercial value. This is a particular problem in processing flax that is harvested for its seeds to produce linseed oil such as grown in North America. The North American strain of flax straw is a shorter plant that matures earlier so that it is cheaper to grow than the longer strains of flax straw which are specifically grown for fiber production, such as in Europe. Accordingly, processing flax straw, particularly of the North American strain requires that the woody portions or shive be separated from the flax fibers without a substantial shortening of the flax fibers given the short length of the flax straw to begin with. However, the equipment employed for this process is typically not specifically designed to handle the short North American strain of flax straw and generally causes too much shortening of the fiber rendering it less desirable for many commercial applications and difficult to process in terms of separating out the shive therefrom. Because of this, in most instances where the flax plant is cultivated for its oilseed in North America, there is no attempt made to process the flax to obtain the fibers therefrom. In 1996 in Canada alone, 2.2 million acres of flax straw were grown. As only approximately 10-20% of this acreage of flax was used for paper processing, it can be seen that there is a huge amount of untapped flax fiber that is not currently being used because of the above-described processing limitations.
The stalk of the flax plant has about 30-40% long outer bast fibers and 60-70% short woody inner core fibers or shives. The shives are left as a by-product when the flax material is processed to separate the fibers therefrom. Accordingly, the majority of the flax plant is left as a low-cost reject that is disposed of without any appreciable commercial gain such as by supplying it to farmers for livestock bedding, or for piling it along treelines as biomass to mix with soil and for stopping weed growth. In this regard, sale of shive material only takes in around $9 per ton. Shive has also been used in some board making, and pulp and paper applications.
The size of the shive separated by flax processing equipment from the fibers thereof can vary widely from small to large pieces of shive. In most current applications for shive, the size of the shive is not critical such that the variations in shive sizes as produced by current flax processing equipment are not an issue. On the other hand, applicants have found that shive that is ground to a fine, consistent size can be used in polymer composite applications as either a filler or a reinforcement additive. As opposed to most current applications where shive is utilized, the size of the shive can be critical in composite applications making the consistency of the small shive particles important.
Thus, it can be seen that there is a need for a plant material processing system, and particularly one that processes the short, tough North American strain of flax grown for its oilseed, that is effective to separate the fibers from the shive thereof without undesirably damaging and shortening the fibers. Further, there is a need for a processing system which can take the shive separated from the flax fibers and reduce it to a very fine, consistent size which has found particular utility in composite applications.
In accordance with the present invention, a system for processing plant material is provided which separates plant fibers from the woody portions of the material to produce a commercially desirable length of fiber and to grind the shorter woody portions that have been separated from the longer fibers to a desirable size which, as described, has found use in certain commercial applications. The current system is well suited to process the tough fibers of the North American strain of flax straw, and will also find utility in processing other bast fibers, such as jute, hemp, ramie, and kenaf.
In one form of the invention, a processing system is provided having a plurality of processing sections which separate woody portions from fibers of plant material and for reducing the size of the separated woody portions. These processing sections include a stripping section for exerting a pulling action on the plant material to strip woody portions therefrom while minimizing damage to and shortening of the fibers. Following the stripping section, a cleaning section is provided for separating the majority of the remaining woody portions associated with the plant fibers by scraping of the plant material to obtain a further separation of the remaining woody material for yielding a product that has a very high fiber purity with the scraping action similar to the stripping action, doing minimal damage to the fiber length so that the fibers remain at a length that is commercially valuable. The woody portions are taken from the stripping and cleaning sections and are then subjected to a grinding section which rapidly beats and grinds the woody portions to a small particle size.
The processing system may include a fiber recovery portion that has an oscillating sieve section for shaking and screening any longer fibers which may have dropped or fallen out of the stripping and cleaning sections along with the woody portions so that substantially only woody portions are fed to the grinding section. To ensure a consistent fine size of the woody portions or shive, a rotary screening section can be provided subsequent to the grinding section with the screening section sifting the woody portions to the commercially desired size such as for use in composite applications.
In one exemplary application of the use of the processing system herein, the plant material, e.g. oilseed flax after removal of the seed therefrom, fed to the stripping section has a length in the range of approximately 12-14 inches and the stripping section produces fibers having a length in the range of approximately 6-8 inches. After being subjected to the cleaning section, the fiber length is reduced to be in the range of approximately 4-6 inches. Accordingly, it can be seen that the fibers produced by the present processing system are kept to a length that is approximately between 30 to 50 percent of the original length of the flax straw that is fed into the processing system.
It should be understood that when discussing sizes of the plant material and the various portions thereof that by necessity these should be considered average sizes given the large volume of plant material that the present system processes. Because of the large volume throughput which the present processing system is designed to handle, e.g. on the order of 10,000 lbs of plant material per hour, there are bound to be variations in the sizes of the plant material and its portions that do not fall within the ranges as specified herein. Nevertheless, the majority of this material has been found to fall within the specified ranges despite minor variations therefrom.
Preferably, the stripping section yields a fiber product that is in the range of approximately 55 to 60 percent fiber purity and the fiber product yielded by cleaning section is further purified to approximately 90 percent fiber purity. Thus, unlike prior processing equipment, the system herein yields a very high percentage for fiber purity while at the same time minimizing the damage and consequent shortening of the fibers so that they are at a commercially desirable length as they exit from the present processing system.
The predetermined size of the woody portions produced by the downstream grinding section can be in the range of between approximately 0.125 inch and 0.020 inch. Where the plant material is flax and the grinding section produces shive to the above specified range of sizes, at this fine size the shive is particularly suitable for use in composite applications, as earlier discussed. More particularly, the shive must be at a consistent size because it must be of sufficient size to provide the reinforcing characteristics that may be desired from it when used in a polymer composite but also be sufficiently small for smooth processing in terms of having good mixing characteristics with the polymer resins and proper melt flow characteristics.
Another aspect of the invention is the provision of a cleaning apparatus for receiving decorticated plant material that has a first level of fiber purity, e.g. 55 to 60% fiber purity, and further separating remaining woody portions from fibers in the decorticated material to increase fiber purity to a second higher level of fiber purity, e.g. 90% fiber purity, over the first level. The apparatus includes at least one set of a cylinder and an associated concave member having a predetermined radial spacing therebetween and through which the plant material travels as the cylinder is rotated. Spikes are provided on the cylinder and the concave member that project generally radially therefrom and which are arranged so that the spikes overlap and are spaced laterally from each other as the cylinder is rotated and the spikes thereon pass the spikes on the concave member. Accordingly, as the cylinder spikes carry plant material past the concave member spikes, the material undergoes a scraping action to further remove any remaining woody portions from the fibers without substantial damage thereto. The spikes on the cylinder and the concave member are of a predetermined length that is slightly less than the predetermined radial spacing between the cylinder and concave member to minimize the radial clearance between the distal tips of the spikes and the cylinder and the concave member. By having the spikes extend to a depth close to the respective surfaces of the cylinder and the concave member, the amount of plant material in the lateral spaces between the respective spike members of the cylinder and the concave member undergoing the aforesaid scraping action is maximized.
Preferably, there are five sets of cylinders and associated concave members provided through which the plant material travels.
The concave member can have a grated section that is downstream and circumferentially rearward of the concave member spikes in the plant material travel direction so that after the plant material carried by the cylinder spikes is subjected to the scraping action against the concave member spikes, the plant material travels over the grated section with scrapped off woody portions of the plant material passing through the grated section. The grated section has openings that are at a predetermined size selected to keep the longer fibers from passing through the openings while permitting the shorter scraped off woody portions to pass therethrough.
As is apparent, it is important for the processing equipment to minimize damage to the fibers so that they remain at a sufficient length for passing over the grated section, as otherwise proper sorting of fibers from separated woody portions will not occur potentially adversely affecting the subsequent processing of the plant material. Accordingly, the size of the grate openings is critical for properly sorting the separated woody portions from the fibers for subsequent processing of the woody portions, as will be discussed more fully hereinafter. In this regard, it is also important that the processing equipment utilized upstream from the cylinder and concave member keep the fibers at a proper length so that the scraping action generated by the spikes of the cylinder and concave member do not shorten the fibers beyond their critical length for passing over the grated section.
The spikes of the cylinder and concave member are preferably arranged in rows circumferentially spaced from one another with adjacent rows having spikes that are offset from each other so that the plant material is caused to undergo a back and forth scraping action as it is successively engages concave member spikes in different rows on either side of a particular cylinder spike. In this manner, the material is not continuously scraped along the same portion thereof throughout the spike overlap area and instead alternatively hits the offset spikes in different rows of the concave members at different times with different portions of the plant material to thereby minimize damage to the length of the fibers while still scraping off the woody portions therefrom.
In another form of the invention, a method of producing fibers from plant material is provided. The method includes stripping woody material from fibers of the plant material to produce decorticated plant material at a first level of fiber purity, providing a plant material scraping area defined by cooperating spikes on a cylinder and associated concave member arranged in a set, feeding the decorticated plant material at the first level of fiber purity to the cylinder and concave member set, rotating the cylinder with the spikes thereon passing the spikes on the concave member with lateral spacing therebetween, carrying the decorticated plant material with the spikes on the cylinder to the scraping area by rotation of the cylinder, scraping woody portions of the plant material from the fibers as the plant material engages spikes on the concave member in the scraping area to minimize shortening of the fibers, and producing fibers at a higher level of purity than the first level after scraping and which are at a length that is only slightly shorter than the fibers fed to the scraping area.
The method may include arranging the spikes on the cylinder and concave member in circumferentially spaced axial rows with spikes in adjacent rows having spikes that are offset from each other, and causing the plant material to undergo a back and forth scraping action as the cylinder spikes carry plant material to the scraping area with the plant material successively engaging offset concave member spikes in different rows on the concave member on either side of a particular cylinder spike.
In another aspect of the invention, a rotary grinder for grinding woody portions separated from fibers of plant material is provided. The rotary grinder includes a rotor and a plurality of pivot shafts fixed to the rotor for rotating therewith. A plurality of flailing members are pivotally mounted on each of the pivot shafts. An inlet to the rotary grinder is provided through which woody portions separated from the plant fibers are fed to the grinder. A screen assembly is spaced from the rotor and has outlet apertures at a predetermined size through which the woody portions are screened during operation of the grinder for producing woody portions that are reduced in size by at least 90 percent from when they enter the grinder. A motor drive is provided for high speed rotation of the rotor with the flailing members pivoted out on their pivot shafts to impact against the woody portions for reducing their size until they can pass through the screen outlet apertures. In a preferred form, the predetermined screen opening size is in the range of 0.125 to 0.020 inch. Accordingly, the above grinder produces woody portions or shive that is ground to a fine, consistent size which can be sold for significant commercial gain for use in composite applications.
In one form, the screen assembly includes a substantially rigid support or backing member having openings that are substantially larger in size than the screen assembly outlet apertures. A flexible screen member includes the outlet apertures and is fixed to the rigid support member so that flailed and ground up woody portions first pass through the outlet apertures and then through the support member openings. The above-described construction of the screen assembly is important because at the high-speed rotation of the rotor and with the large amount of woody portions or shive material that are being fed through the inlet of the grinder, there are significant forces developed as the flailing members impact against the shive until they are reduced to a size sufficiently small so that they can pass through the screen outlet apertures. As the screen including the very small sized apertures is flexible, without use of the more rigid backing member, the flexible screen would likely fail under applied forces during operation of the rotary grinder. On the other hand, the screen assembly with the rigid backing member is effective to allow use of the finer flexible screen member for producing the desired size of shive while still processing high volumes of shive material through the grinder.
In another aspect of the invention, a method of producing finely sized woody portions of plant material is provided. The method includes stripping and scraping woody portions from fibers of the plant material, providing a first rotary grinder having a rotor and pivotally mounted flailing members and outlet apertures at a first small predetermined size, feeding the woody portions that have been stripped and scraped from the plant fibers to the first rotary grinder, driving the grinder rotor for high speed rotation so that the flailing members are pivoted out from the rotor, impacting the woody portions with the pivoted out flailing members, and reducing the size of the woody portions to the first predetermined size of the outlet apertures for passing therethrough as an incident of being impacted with the flailing members.
The method may further include providing a second rotary grinder having a rotor and pivotally mounted flailing member and outlet apertures at a second predetermined size that is smaller than the first predetermined size, feeding the reduced size woody portions from the first rotary grinder to the second rotary grinder, driving the second grinder rotor for high speed rotation so that its flailing members are pivoted out from the rotor, and impacting the reduced size woody portions to the second predetermined smaller size of the second grinder outlet apertures for passing therethrough.
In a preferred form, the method further includes providing a rotary cylindrical screen having apertures at a third predetermined size substantially the same or slightly smaller than the second predetermined size of the outlet apertures of the rotary grinder, feeding the reduced size woody portions from the rotary grinder into the cylindrical screen, rotating the cylindrical screen for passing woody portions that are at or below the third predetermined size through the screen, and recirculating woody portions that do not pass through the screen to the first rotary grinder. In this manner, a continuous loop is provided for processing all of the woody portions or shive from the plant material and reducing it to the desired size for commercial sale. With this method, the shive material that was sold for little commercial gain is efficiently processed to the appropriate size without losing shive during the processing stages so that substantially all of the flax plant material is sold for commercial gain.